A thermal flow meter that measure a flow rate of gas is configured to include an air flow sensing portion for measuring a flow rate, such that a flow rate of the gas is measured by performing heat transfer between the air flow sensing portion and the gas as a measurement target. The flow rate measured by the thermal flow meter is widely used as an important control parameter for various devices. The thermal flow meter is characterized in that a flow rate of gas such as a mass flow rate can be measured with relatively high accuracy, compared to other types of flow meters.
However, it is desirable to further improve the measurement accuracy of the gas flow rate. For example, in a vehicle where an internal combustion engine is mounted, demands for fuel saving or exhaust gas purification are high. In order to satisfy such demands, it is desirable to measure the intake air amount which is a main parameter of the internal combustion engine with high accuracy.
In a conventional thermal flow rate sensor, a sealing resin covering a sensor chip is provided to cover the sensor chip in such a manner as to be in contact with, at least, a side surface which is perpendicular to a heat generator formation surface of the sensor chip and which is an upstream-side portion with respect to an air flow sensing portion in terms of flow of fluid, and that the heat generator formation surface of the sensor chip and the side-surface covered part of the sealing resin are flush with each other in a direction perpendicular to the heat generator formation surface (see, for example, PTL 1).